The present invention relates to methods for use of oil-soluble weighting agents in subterranean formation treatment fluids.
Subterranean formation treatment fluids (also referred to herein as “treatment fluids”) may be used in various capacities during the drilling, completion, and/or production of an oil and gas well, such drilling operations, as lost circulation operations, sand control operations, fracturing operations, frac-packing operations, gravel packing operations, and the like (also referred to herein as “subterranean operations”). Many of these operations require the treatment fluids to possess a density sufficient to suspend particulates, such as drill cuttings, formation fines, and proppant particulates, for example. As such, it has long been desired that treatment fluids possess sufficient density to suspend such particulates. Moreover, the density of a treatment fluid contributes to the stability of a wellbore by increasing the pressure exerted by the treatment fluid onto the surface of the subterranean formation so as to prevent undesirable inflow of reservoir fluids into the wellbore.
In order to increase the density of treatment fluids, weighting agents are typically added to the fluids. However, the use of treatment fluids comprising weighting agents during the drilling, completion, and/or production of oil and gas wells often results in sedimentation or “sag.” Sag is characterized by the settling out of the weighting agents from the treatment fluids, resulting in density variations throughout the treatment fluid (i.e., some portions of the treatment fluids have higher than desirable densities and some portions of the treatment fluids have lower than desirable densities). Sag may lead to numerous issues such as lost circulation, cementing problems, collapsed pipe, and the like and may be caused by various operational factors, such as well design, the mass of the weighting agents, the formulations of the treatment fluid, and the like.
In order to combat the sag phenomenon, soluble weighting agents have been developed for aqueous base fluids, including salt based weighting agents. These soluble weighting agents increase the density of the aqueous base fluids but, because they are solubilized, they do not face the problems (such as settling and sag) common to particulate weighting agents. These soluble weighting agents have proven very effective for use in aqueous treatment fluids. However, subterranean operations often benefit from the use of oil-based (including oil emulsion) treatment fluids. These treatment fluids are incapable of solubilizing the soluble weighting agents that are compatible with aqueous base fluids. Therefore, a method of increasing the density of an oil-based treatment fluid with a soluble weighting agent may be of benefit to one of ordinary skill in the art.